Many computing and electronic devices store information using magnetic media, such as hard disk drives. Generally, the information is stored by encoding the information into a series of bits and then writing the encoded bits to a layer of magnetic material on one or more disks of magnetic media. To do so, a read-write head of the media drive produces, based on values of the encoded bits, a magnetic field strong enough to polarize small portions of the magnetic media. As the disk coated in magnetic media turns below the read-write head, the changing magnetic field of the read-write head imparts different polarities to respective sections of the magnetic media that correspond to the series of encoded bits. In other words, the read-write head writes a sequence of ones and zeros into the magnetic media as a corresponding sequence of north-south or south-north magnetic polarities.
To read the information from the magnetic media disk, the read-write head picks-up or senses the polarity variations from a surface of the magnetic media. Signals associated with sensing polarity of each section of the magnetic media, however, are often weak or vary greatly depending on characteristics of the magnetic media or a position of the read-write head relative the magnetic media disk. To address these issues, many media drives include an amplifier circuit to amplify the signal provided by the read-write head by varying levels before attempting to decode the signal in order to determine the sequence of bits that were previously written to the magnetic media.
Amplifying the signals at low levels of gain, however, reduces phase margin of some amplifiers with feedback circuitry and necessitates an increase in compensation capacitance to maintain stability of the amplifier circuit. Although compensation capacitors can be added to maintain amplifier stability, a large number of capacitors and complex switching circuitry are typically needed to achieve sufficient compensation over wide ranges of gain adjustment. Further, with compensation capacitors of discrete capacitance values, the provided compensation capacitance is suboptimal across all but a few select gain levels, resulting in a loss of amplifier bandwidth due to over compensation. These and other issues associated with switching in capacitors of different capacitance values, which disrupts the compensation, often result in glitches at the amplifiers output and incorrect operation of amplifier gain control.
The background description provided herein is for the purpose of generally presenting the context of the disclosure. Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.